Loop erection system



March 26, 1968 N. o. YOUNG LOOP ERECTION SYSTEM 2 Sheets-Sheet 1 Filed Aug. 15, 1966 INVENTOR. Niels 0. Young RM 'rforney March 26, 1968 N. o. YOUNG 3,374,933

L003 ERECTION SYSTEM Filed Aug. 15, 1966 2 Sheets-Sheet 2 OUT TO STORAGE OUT TO IN FROM STANDING LOOP STANDING LOOP Flg. 2

INVENTOR. Niels 0. Young BY Rewk smu A torney United States Patent Ofifice 3,374,933 Patented Mar. 26, 1968 3,374,933 LOOP ERECTION SYSTEM Niels 0. Young, Lincoln, Mass., assignor to Block Engineering, Inc., Cambridge, Mass., a corporation of Delaware Filed Aug. 15, 1966, Ser. No. 572,557 11 Claims. (Cl. 226118) This invention relates to erecting systems and more particularly to means for erecting a flexible, closed loop into a substantially stiff, apparently rigid structure.

Under ordinary circumstances, a flexible or limp loop of material cannot assume a self-supporting configuration if it is completely compliant, i.e. lacks stiffness. Ordinarily, the shape and size in which a flexible loop can be selfsupporting depends largely upon the extent to which its degree of stiffness opposes loading, such as would be due to gravity.

However, a compliant, flexible, closed loop moved along itself, at sufiicient speed provides an appearance of mechanical stiffness and can thus be erected to form a substantially rigid-appearing, self-supporting structure capable of astonishing extension.

Generally, such systems comprise an elongated flexible element or line-mass formed into an endless or closed loop, a guide in which a portion of the loop is mounted so that the loop is freely movable substantially longitudinally along the guide, and means for moving the loop through the guide with speed sufficient to cause the portion of the loop not constrained by the guide to erect into a substantially rigid structure.'

If the loop circumference is large compared to the guide, the loop, when erected, assumes an elongatedform. It is difficult to erect long loops where no constrain exists other than is provided by the guide, there being a tendency for initially unerected portions of the loop to'tangle on erection, or because of friction effects between unerected portions with one another or with some support or container.

A principal object of the present invention is to provide an erection system for such a loop, operable to erect the loop into a substantially rigid-appearing, elongated configuration of controllable height.

Other objects of the present invention are to provide such an erection system including a storage syster'nfor holding a variable portion of the loop material, which storage obviates the previously noted problems arising when it is desired to erect very long loops; and to provide, in conjunction with such a variable quantity storage system, drive means for moving or propelling the loop material at sutficient speed to cause erection into a free-standing loop structure. 7

Such loop erection and storage systems have a number of diverse uses. For example, if the loop is formed of an electrically conducting line mass or metallic wire, it can be readily employed as an antenna capable of erection wherever an open area and a rotary motor of suflicient power is available. Other uses are to generate high potentials in a Van De Graaf mode, investigation of cloud potentials, and the like.

Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements, and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the present invention, referencev should be had to the following detailed description taken in connection with the accompanying drawing wherein FIG. 1 is an elevational view, partly in cross-section through an apparatus embodying the principles of the present invention; and

FIG. 2 is a top plan view, in section, of the drive and guide means of FIG. 1.

Referring now to the drawing there is shown a form of the present invention including flexible, continuous, closed loop means 20, only portions of which are shown, storage means22 for storing a variable proportion of the loop means, and means 24 for driving and guiding the loop.

Closed loop 20 can be formed of any of a large number of materials capable of being extended into line-mass configuration. For example, the loop can be a rope or string of fibrous material such as linen, rayon, hemp, cotton, or the like; a metallic cable of copper, steel, or mixed metalpolymer material, in continuous extended form, braided, twisted or the like; a string or chain of links or beads formed of hollow metallic or polymeric materials, etc. The cross-section shape of the loop line-mass is not very important, and indeed flat tape will serve, although for purposes of illustration, the loop is shown as a cable.

Storage and guide means 22 comprise an enclosure or support such as rigid frame 26 in a substantially rectangular shape having an open or hollow interior. Mounted on a top portion 28 of frame 26 and extending toward the interior of the frame in spaced apart relation to one another are a pair of bearing blocks 30 and 32 having a freely rotatable shaft 34 journaled and suspended therebetween. Coaxially mounted on shaft 34 is a plurality of n sheaves 36 each of substantially the same diameter, the sheaves being independently rotatable with respect to one another about shaft 34. The sheaves are positioned closely adjacent one another to form a first sheave array 38. in which the sheaves are held in closely spaced relation by a pair of retainer discs 40 and 42 fixed to the shaft adjacent each end of array 38.

Extending across the interior of frame 26 is a pair of guide means or elongated slide rods 44 and 46 firmly fixed or bolted to the ends of frame and positioned substantially parallel to one another in spaced apart relation greater than the length of array 3 8'. Slidably mounted on and extending between rods 44 and 46 is end plate 48. Mounted on plate 48 and also slidably mounted on rod 46 is sliding bearing block 50 a similar bearing block 52 being also mounted on plate 48 spaced from block 50. Suspended between blocks 50 and 52 and journaled into both of the latter is rotatable shaft 54. There is provided a second plurality of n' independently rotatable sheaves 56 which are mounted coaxially on shaft 54, the sheaves being closely adjacent one another to form a second array 58 held in position by retainer plates 60 and '62 respectively aflixed to shaft 54 adjacent the ends of the second array.

It will be apparent that while first array 38 is mounted on a shaft which is fixed to the frame, second array 58 is mounted on a carriage formed of plate 48, hearing blocks 50' and 52 and shaft 54 so as to be moveable within the frame. The carriage thus formed is slidably moveable along rods 44 and 46, toward and away from array 38, with shaft 54 being maintained substantially parallel to shaft 34. Because at least bearing block 50 is slidably mounted on rod 44 at two spaced points, the carriage is constrained to move only along the rod and cannot wobble. Sliding connection of plate 4 8 with rods 44 and 46 can be through perforations in the plate or by forming the plate ends as forks. Carriage plate 48 is connected to end 64 of frame 26 opposite to end 28 by negator spring.

66 so as to be normally loaded for movement away from array 38. Negator springs, well known in the art, are of the type which provide a substantially constant spring load regardless of the extension of the spring.

Provided in frame at positions immediately adjacent the two end sheaves of array 38 are outlet opening 68 and inlet opening 70. A portion of loop 20 shown at 20A is threaded into the interior of frame 26 through opening 68, passes around an end sheave of array 38 immediately adjacent opening 70, then to the corresponding end sheave of array 58 around the latter and back to the next successive sheave of array 38, around the latter and then to the next successive sheave of array 58 and so on. It will be apparent then that portion 20A of loop 20 forms a helical winding in which each loop of the winding embraces a pair of sheaves 3'8 and 58. Portion 20A of the loop at the last helical Winding leaves the other end sheave of array 58 and engages the corresponding end sheave of array 38 from whence it passes outwardly through opening 70.

Now assuming that 11:50, and that all the sheaves of the arrays have the same diameter D, the smallest length of portion 20A of the loop which will be stored on the two arrays of sheaves is 50(1rD-i-2A) where A is the minimum spacing between the two shafts 34 and 54 established by stop means (not shown). Assuming that the carriage bearing the second array of sheaves can move to increase A by an increment S i.e. the depth of the frame is sufiicient to allow negator spring 66 to pull the carriage S units of length toward the bottom of the frame, then the maximum length of the portion 20A of loop 20 which can be stored on the two array of sheaves is then 50(1rD+2(A|-S)). Using typical values where D is one foot, A is thirteen inches, and S is three feet, it will be seen that the maximum length of portion 20A of the loop stored is about 565 feet, whilst the minimum storage is about 265 feet, a difference of about 400 feet. This then permits the length of loop not stored on the sheave to vary by approximately 200 feet as measured along its axis of elongation.

Drive means 24 is intended to impart continuously to one side of the closed loop a predetermined force for driving the loop in rotation above a certain velocity such that the free portion of the loop shown at 20B (i.e. the part unconstrained by either storage means 22 or drive means 24) will extend into an elongated, apparently rigid, self-supporting configuration.

To this end, drive and guide means 24 shown for convenience in section comprises cylindrical hollow main support 72 firmly afiixed atop frame portion 28 as by support legs 74 and 76. Mounted for rotation in support 72 on bearings 78 is drive shaft 80 which extends outwardly through both ends of support 72. Connected to one end of shaft 80 for rotation therewith is first capstan or drum 82 positioned above outlet opening 68. Connected adjacent to other end of shaft 80 for rotation therewith and this with drum 82 is second capstan 84. The latter preferably is of slightly smaller diameter than capstan 82.

As shown, shaft 80 is coupleable to a source of mechanical rotational power, hence extends through the center of rotation of drum '84 and can be coupled thereat as by compliant linkage or universal coupling 86 to shaft 88 of a motor.

Now it is intended that loop 20 be fed out of opening 68 and wound at least one full turn (preferably more) around drum 82 which, in turning, supplies the thrust to drive the loop into erection. However, as is well known, a string or cord wound around and driven by a drum tends to creep, or screw along the drum surface and must be constrained lest it fall off of the drum.

Further, the thrust of the drum is tangential and is not limited to any particular direction with respect to the entire apparaus. Hence, there is preferably provided guide means, shown generally at 90 for limiting the motion of the turns of loop 20 with respect to the axial direction of the drum and more importantly for limiting the direction along which the tangential thrust of the drum drives the loop as it leaves the drum. Guide m a s 90 th r f i in the form of an enclosure fixedly mounted as on leg 74 and surrounding drum 82. Guide means includes inlet aperture '92 facing outlet opening 68 and outlet aperture 94 so that a line through aperture 92 and opening 68 will be tangent to the drum, preferably located on the opposite side of the enclosure. and offset by the dis tance axially along the drum occupied by the turns of loop 20 wound around the drum. The interior walls of the guide means then serve as a constraint on axial motion of the turns on the drum. Both apertures 92 and 94 preferably have rounded edges so as to minimize friction between the aperture walls and the loop passing therethrough.

Surrounding drum 84 is a similar guide means such as enclosure 96 having outlet aperture 98 facing inlet opening 70 such that a line extending tangent to the drum will pass through both. On the opposite side of enclossure 96 is inlet aperture 100 appropriately offset.

As will appear hereinafter, it is preferred that under certain circumstances, the turns of loop 20 around drum 82 be allowed to slip, hence the surface of the latter can exhibit a low coefficient of friction with respect to the loop. However, when it is wished to impart maximum thrust to the loop, slippage is undesirable. Hence, as shown in FIG. 2, means are provided for selectively imparting a radially inward (with respect to the drum) force on a turn of the loop about the drum, thereby insuring that no slippage will occur. For this purpose, enclosure 90 includes opening 102 therein in which is disposed axially movable rod 104,0ne end of which can be moved into a position wherein it provides transverse pressure onto a portion of loop 20 wound around drum 82. Rod 104 is preferably provided with means, such as spring 106 for resiliently biasing the rod out of its contact position with loop 20. In another form, rod 104 can include a wheel at its contact end to reduce sliding friction between the rod and loop. Also rod 104 can be elect-romagnetically actuated as a relay armature rather than manually as shown. To describe the operation of the device, it can be assumed that under the influence of negator spring 66-, the carriage bearing sheave array 58 is at its maximum distance from array 38, hence, that storage device 22 contains the largest amount of loop possible. Power applied to shaft 80 will cause the drum to rotate. Upon depressing rod 104 against the bias of spring 106, loop 20 Wound around drum 82 is forced into contact with the latter and an axial thrust is imparted to the loop, thereby driving the loop out of aperture 94. "If the speed of the loop is suflicient, the loop will assume a self-supporting configura tion.

Now, if the frictional drag of drum 82 on loop 20 exceeds the combined frictional effects of the mounting of sheaves 36 and 56 and the force exerted by spring 66, portion 208 of the loop will grow in extenison upwardly, the amount of loop stored in device 22 correspondingly becoming lesser as array 58 is drawn upwardly toward array 38.

'Because take-up drum 84 is smaller in diameter than drive drum 82, the torque on loop portion 20B due to drum 84 is always lesser than the torque applied by drum 82. Thus, loop portion 208 always has a net driving force thereon when the drums are rotating. Of course, the turns of the loop around drum 84 can readily slip if necessary to keep the loop moving at the same speed around drum 84 as the speed with which it leaves drum 82.

Now, if the speed of shaft -80 is reduced, the forces can be predetermined such that negator spring 66 can overcome the thrustforce of drum 82 whilst the speed of loop 20 is still maintained at sufiicient magnitude to keep loop portion 20B in erection. In such case, the force of spring 66 draws array 58 away from array 38 reducing the extent of elongation of loop portion 20 B. Should one desire to stop the drums completely while loop 20 is moving, it is necessary to disengage rod 104. This per mits the loop, under the impetus of its own inertia to keep moving, because it now slips around drum 82. Spring 66 will cause the loop to be stored as the loop slows down. Thus, preventing tangling or snarling.

Now it can be demonstrated that the apparent rigidity of the loop, i.e. the ability of the loop to be self-supporting, depends upon its own motion substantially along its longitudinal dimension and not on support provided by drive and guide means 24. The peculiar behaviour of the loop might be viewed as a case of exterior ballistics such as where a gun recycles a line of connected projectiles in a closed loop. However, exterior ballistics deals with isolated point masses accelerated by gravity and air forces; in the loop of the present invention, although subject to gravity and air forces, each element is not isolated but interacts with the whole trajectory and has a nearly constant speed along the trajectory. Therefore, the kinetic energy of each element of the line-mass cannot be traded for geopotential in the usual way.

According to a more analytical approach, it is believed that the phenomenon observed occurs because the string or line-mass is under tension generated by its own motion. Consider an element of the line mass moving at speed V with respect to a space curve along an arc of radius R. The mass m of the element is then equal to PRd for a line mass of density P and increment of arc length d0. By motion along the arc, a tension 0' is developed such that 2 1 a da g or by substitution Interestingly, Equation 2 indicates that the tension developed is independent of local curvature.

'Now for a loop standing up to a height h, the compressive stress, er generated by the weight of the line mass would be where g is the acceleration due to gravity.

Since the string cannot endure compression without collapsing, being to some extent compliant, then for the string to be self-supporting, a' must be greater than c or In other words, the kinetic energy of the line-mass must always exceed its gravitational potential energy for the loop to be in erection.

Finally, consider the moving line-mass to be stabilized along the space curve by wave-motion. The speed V of a lateral wave along the line-mass is then :(u/p) From Equation 2 it then appears that Vr=|V and the space curved line-mass can be considered a standing wave of speed VV The apparent rigidity of the space curved line-mass can be considered then as rising from waves propagating at a velocity V+V This appears to explain certain effects observed in the behaviour of such standing loops. For example, a displacement aplied transversely of the line-mass appears to be communicated by such fast waves to the entire loop. Thus, the string follows translations of the device as if it were almost a rigid structure. Rotation of the device about the axis of elongation of the standing lOOp reveals effects which seem gyroscopic. If so rotated, the string forms a helix having a plurality of turns, although the upper bight of the loop tends to maintain its original orientation. When this rotation of the device is stopped, the upper bight appears to precess, slowly turning and unwinding the helix until the loop again lies substantially in a single plane.

Weights can be lifited by the upper bight of a standing loop since a thrust is observed on a flat plate touching the bight. Hence, a rider can be supported by the loop, but

this tends to create an unstable situation due to a standing wave which forms before the rider.

Two modes of operation of the loop are observable. There is a low velocity mode wherein the loop will need to have a portion of its weight supported by a surface, and a high velocity mode in which the loop weight will be totally self-supporting. The transition velocity between these two modes can be determined by considering that to reach the high velocity mode, the weight of the string must be supported by the thrust of the string drive. However, the drive thrust must at least be equal to air drag on the string and hence at transition, the string must be moving at its terminal velocity V, defined as follows:

( gay P,,C' where P and P are respectively the density of the string and of air, g is the acceleration of gravity, and C is the drag coefiicient for the string in axial flow.

Thus, aerodynamic effects are of importance in stabilizing the standing loop. For line-mass velocities greater than terminal there are slow waves rather than standing waves which propagate out to the upper bight. The velocity of these waves increases with string velocity. To explain this, consider rotating the drive means transversely to the long loop axis. The existing angular momentum of the whole loop must re-orient to the new pointing direction. Since only negligible torques can be exerted by the drive, the required torque can only come from air drag forces acting along the string. Now the angular momentum is proportional to V while the drag forces are proportional to V Therefore, the whole loop should IC- orient faster for greater V, as is indeed observed.

The internal friction and spring rate of the string in bending, influence the shape of the space curve of the standing loop. In general, the stiffer the string or cord, the larger the radius of the upper bight. For example, the

stiffness of tightly laid nylon cord makes it possible to operate a standing loop only for heights exceeding about 200 times the cord diameter.

Power is required to operate a standing loop in air. At the terminal velocity of the string it is minimally stable, and the power required is simply the cord weight times its velocity. Considering the cord density and weight as the only variables in Equation 5 observe that the power required is proportional to the cord weight times the square root of its density. The power required can of course be reduced by using a cord of low weight and density. Power calculated in this fashion agrees with observation.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved it is intended that all matter contained in the above-description or shown in the accompanying drawing shall be interpreted in an illustrative and not in a limiting sense.

What is claimed is:

1. An erection device comprising, in combination,

an elongated flexible element forming a closed loop;

guide means providing a constraining path for a portion of said loop so that said element is movable substantially along its longitudinal axis in said. path at said guide means;

means for holding a variable proportion of said element in ordered storage, the remainder of the loop not in said guide means or in storage being unconstrained, and

means for providing a thrust to said element along said path to impart speed to said element sufiicient to cause said unconstrained remainder of said loop to erect into a substantially rigid structure.

2. An erection device as defined in claim 1 wherein said means providing a thrust comprises;

first means having a first movable surface, at least a portion of said element being positioned for engagement with said surface for driving the latter out of said means for holding said element in storage.

3. An erection device as defined in claim 2 wherein said means providing a thrust comprises second means having a second movable surface, of at least a portion of said element being positioned for engagement with said second movable surface so as to be guided by the latter into said storage means, said surfaces being movable at different speeds so that said element can be driven out of said storage means at a rate different than said element is guided into said storage means.

4. An erection device as defined in claim 2 wherein said constraining path defined by said guide means is substantially tangential to said first movable surface.

5. An erection device as defined in claim 2 including means for selectively exerting a radial force against said portion of said element sufiicient to cause said first surface, when moving, to engage said portion frictionally without substantial slippage, said first surface and the surface of said element being characterized by substantially slipping with respect to one another when said 'first surface is moving and said radial force is not being exerted.

6. An erection device as defined in claim 1 wherein said means for holding said element in storage comprises a first array of rotatable sheaves and a second array of rotatable sheaves, and

means for supporting said arrays so that said arrays are movable with respect to one another.

7. An erection device as defined in claim 6 wherein a portion of said element is alternatively wound around sheaves of said first array and corresponding sheaves of said second array.

8. An erection device as defined in claim 6 wherein the sheaves of said first array are substantially coaxial along a first axis and the sheaves of said second array are substantially coaxial along a second axis, and said means for supporting said arrays includes means fixedly positioning said first axis and means supporting said second array so that said second axis is approximately parallel to and movable transversely of said first axis.

9. An erection device as defined in claim 8 including means for maintaining the two said axes in parallelism during movement of said second array.

10. An erection device as defined in claim 9 including means for resiliently biasing said second array for movement away from said first array.

11. An erection device as defined in claim 10 wherein said means for resiliently biasing exerts a force less than any force exerted on said second array by said element due to said thrust and greater than any force exerted on said second array by said element in the absence of said thrust.

References Cited UNITED STATES PATENTS 3,299,538 1/1967 Cooper 226--118 X EVON C. BLUNK, Primary Examiner.

M. L. AIEMAN, Assistant Examiner. 

1. AN ERECTION DEVICE COMPRISING, IN COMBINATION, AN ELONGATED FLEXIBLE ELEMENT FORMING A CLOSE LOOP; GUIDE MEANS PROVIDING A CONSTRAINING PATH FOR A PORTION OF SAID LOOP SO THAT SAID ELEMENT IS MOVABLE SUBSTANTIALLY ALONG ITS LONGITUDINAL AXIS IN SAID PATH AT SAID GUIDE MEANS; MEANS FOR HOLDING A VARIABLE PROPORTION OF SAID ELEMENT IN ORDERED STORAGE, THE REMAINDER OF THE LOOP NOT IN SAID GUIDE MEANS OR IN STORAGE BEING UNCONSTRAINED, AND MEANS FOR PROVIDING A THRUST TO SAID ELEMENT ALONG SAID PATH TO IMPART SPEED TO SAID ELEMENT SUFFICIENT TO CAUSE SAID UNCONSTRAINED REMAINDER OF SAID LOOP TO ERECT INTO A SUBSTANTIALLY RIGID STRUCTURE. 